Vanessa is 3 times as old as Kevin and is also 20 years older than Kevin. How old is Vanessa?
Solution: We can use the given information to write down two equations that describe the ages of Vanessa and Kevin. Let Vanessa's current age be $v$ and Kevin's current age be $k$ $v = 3k$ $v = k + 20$ Now we have two independent equations, and we can solve for our two unknowns. One way to solve for $v$ is to solve the second equation for $k$ and substitute that value into the first equation. Solving our second equation for $k$ , we get: $k = v - 20$ . Substituting this into our first equation, we get the equation: $v = 3$ $(v - 20)$ which combines the information about $v$ from both of our original equations. Simplifying the right side of this equation, we get: $v = 3v - 60$ Solving for $v$ , we get: $2 v = 60$ $v = 30$.